Scientific Method —

New elastic polymer self-heals in just one minute

A self-healing elastomeric polymer can seal up cuts after about one minute …

Self-healing polymers are extremely sought after by scientists, as they have many useful—not to mention lucrative—applications. Back in 2009, we reported a polyurethane-based polymeric material that heals itself in roughly an hour when exposed to UV light. That particular polymer, made by Biswajit Ghosh and Marek W. Urban, would be useful as a protective coating for phones, cars, etc. It worked based on the principle of having a reactive chemical component that would split open when physically damaged to create two reactive ends that can then covalently link together under UV light to repair itself.

In a recent issue of Nature, Mark Burnworth and his colleagues report a different type of self-healing material, one that can repair itself in about a minute under UV light. Burnworth’s polymeric material also doesn’t function on the basis of forming chemical bonds between organic compounds for repair. Instead, it relies on localized heating and metal-ligand interactions.

Burnworth and his team used rubbery oligomers, poly(ethylene-co-butylene), as the core of their material. They attached ligands, 2,6-bis(1’-methylbenzimidazolyl)pyridine (Mebip), that can bind to metals at the ends of the oligomers. To form long polymers, the researchers added either zinc (Zn2+) or lanthanum (La3+) ions to the solution of oligomers. The metal ions form metal-ligand complexes with the Mebip, linking the oligomers with one another.

For their self-healing tests, Burnworth and his team shaped the polymers into films that were 350 to 400 µM thick. They purposefully cut the polymer to about 50 to 70 percent of the overall thickness of the film. When the cuts were exposed to two consecutive 30-second rounds of UV light (320 to 390 nm wavelength at an intensity of 950 mW cm-2), the cuts sealed up. The healed material was comparable in toughness to the original polymeric film, and images from atomic force spectroscopy show that the cuts essentially disappeared.

This process works because complexes of Mebip with metals are chromophoric, so they can absorb light of a specific wavelength, such as light in the UV range. Once they absorb light, they get into a higher energetic state and then lose that energy by giving off heat. Thus, when the researchers exposed the cuts to UV light, there was heating at the surface of the polymeric film—enough heating to reach over 220°C in 30 seconds. The heat quickly depolymerizes the area around the cut. Once the UV light is turned off, the liquidized area cools, reforms the ligand-metal complexes, and seals up the cut.

The healing process can be localized, as you only need to hit damaged areas with UV light. The researchers also show that the healing process would still work if the polymer was under a load of about 8 kPa. They suggest that different ligands could be used to cover a range of absorbable wavelengths. Thus, you could selectively tailor the wavelength of light to heal different types of damaged materials.

Burnworth and his colleagues have made a significant step in getting us closer to having self-healing polymers on the market. Their approach is quite different than that of Ghosh and Urban, which we described previously. While Burnworth’s method certainly heals quicker, it also produces a dramatic increase in surface temperature during healing. Such a huge temperature surge could be disadvantageous for certain applications.

Listing image by Dominique Bersier and Gina Fiore for Adolphe Merkle Institute, Case Western Reserve University, US Army Research Laboratory.

Yun Xie
Yun Xie / Yun Xie is a contributing science writer at Ars, where she covers the latest advancements in science and technology for Ars. She currently works in scientific communications, policy, and review. Emailreenxie@gmail.com//Twitter@yun_xie

Technical facts are great, but I'd like Ars to shed more (UV) light on potential applications of self-healing materials like this. As a consumer, that is what I am interested in.

...This is the "SCIENCE" blog. Not the "Consumer Products" blog. I for one am glad there is at least ONE tech website on the net that has quality researches and journalists. All those OTHER sites just gives basic propaganda that they get from either the company themselves or copy and paste from other sites (see all THOSE sites that have "Hit the source link at the bottom for more")

Technical facts are great, but I'd like Ars to shed more (UV) light on potential applications of self-healing materials like this. As a consumer, that is what I am interested in.

Self-repairing replicators! Our lives as we know them are over.Seriously though, I doubt it is ready for the consumer market, being as brand new as it is. The nature article will be mostly about it's successes, but there will be problems as well.

This will probably end up used only in military applications, and even there with severe artificial limitations. Consumerism is just too damn profitable to forgo for the sake of technological advances.

Technical facts are great, but I'd like Ars to shed more (UV) light on potential applications of self-healing materials like this. As a consumer, that is what I am interested in.

What I would really like is some sort of annual followup. I keep hearing about cool new techs, and then never seeing them (or perhaps I do see them and don't realize). Something that said "Here are the techs we've covered in the last ten years. This one turned out be a failure, this other one is still in testing, this one over here is now in your new phone and this is how they used it, etc..."

This will probably end up used only in military applications, and even there with severe artificial limitations. Consumerism is just too damn profitable to forgo for the sake of technological advances.

If you think self healing armor or something like that, then I doubt, the healing process is too slow and these materials are probably too weak to be used in military anyway. But as a protective coating for cars, motorcycles, sports and outdoor equipment it'd be great.

As a layman, this doesn't sound extremely different to ultrasonic welding. Two pieces of material (or let us say one piece of material with a tear) are joined by the application of energy that creates heat in the materials.

Let's say (commercial application alert!) you have a stealth coating on an aircraft made of this described polymer, and to function optimally, it is perfectly smooth. I'd imagine that after nicks and cuts and wear, you'd land the plane, stick it under a blacklight, and you get a nice glossy coat every time, right? Similarly, if another material like a plastic with a melting point of 220C was landed, and parked in a hangar, you could judiciously apply some heat to it to get the same result.

This will probably end up used only in military applications, and even there with severe artificial limitations. Consumerism is just too damn profitable to forgo for the sake of technological advances.

I'm assuming this was dry sarcasm, but it was so dry that the humor seems to have slipped out.

Fascinating stuff. Makes me wish I'd not bailed on chemistry as a profession!

I hope I'm wrong but it seems like it would take decades of development to get this stuff commercialized. Military applications would make sense first. I wonder how many 'cycles' of tear-repair they could get this up to. Seems like that would be the barrier to commercial utility.

We need the materials to self-detect damage. This material still requires us to either "shoot our wad" and UV irradiate an entire surface or else locate the damage ourselves. The current research isn't so much more useful than applying a "patch" or "respray" to a damaged area, since we have to know where to fix. Maybe it'll dovetail into damage detection later.

I'm confused about the application of such a material. If UV light is simply melting the polymer back to together, wouldn't constant UV light from the sun keep the polymer is "melting" form and prevent it from cooling to form the heal? Or would the heal require a special, higher power UV source specifically for healing cuts? How would consumers access such a (possibly dangerous) device?

What seems odd to me is, why is this better than any high temperature thermoplastic (which is what this seems to me, well that plus high UV absorbtion), that you selectively heat up the damaged area with umm.. maybe a laser, or one hell of a heat gun.

We need the materials to self-detect damage. This material still requires us to either "shoot our wad" and UV irradiate an entire surface or else locate the damage ourselves. The current research isn't so much more useful than applying a "patch" or "respray" to a damaged area, since we have to know where to fix. Maybe it'll dovetail into damage detection later.

Run fine wires through your plastic, pulse the wires, and when you get a reflection you have a break and you can figure where it is.

We need the materials to self-detect damage. This material still requires us to either "shoot our wad" and UV irradiate an entire surface or else locate the damage ourselves. The current research isn't so much more useful than applying a "patch" or "respray" to a damaged area, since we have to know where to fix. Maybe it'll dovetail into damage detection later.

Run fine wires through your plastic, pulse the wires, and when you get a reflection you have a break and you can figure where it is.

Technical facts are great, but I'd like Ars to shed more (UV) light on potential applications of self-healing materials like this. As a consumer, that is what I am interested in.

What I would really like is some sort of annual followup. I keep hearing about cool new techs, and then never seeing them (or perhaps I do see them and don't realize). Something that said "Here are the techs we've covered in the last ten years. This one turned out be a failure, this other one is still in testing, this one over here is now in your new phone and this is how they used it, etc..."

That would actually be pretty cool. Not sure this is the right section for it, but I also keep remember cool stuff you read about and then nothing. Like active camoflage, induction charging, stuff like that. Some of it is slowly turning up, but a lot of it (the ones I don't remember likely ) just seem to fizzle out.

Kinda a bummer when an article sold some brilliant tech like it's going to change the world, and 5 years later we still get incremental updates to existing tech.Even OLED with flexible, damage resistant screens, incredible contrast and color and thin as paper haven't materialized in any real way despite being "just around the corner" for half a decade.

So yeah, an article that took a lot of tech that was heralded as "the new coolness" and looked at where it went would be REALLY cool. The trouble would be figuring out what to write about - some of the research has probably resulted in actual products, but they were just less spectacular than they might have sounded.Like nano-coatings, that made it sound like clothes and furniture would never really get dirty again since nano-tech would protect!! I have some nono-coating spray for my shoes and it works but it's not exactly the miracle that articles made it sound like.

We need the materials to self-detect damage. This material still requires us to either "shoot our wad" and UV irradiate an entire surface or else locate the damage ourselves. The current research isn't so much more useful than applying a "patch" or "respray" to a damaged area, since we have to know where to fix. Maybe it'll dovetail into damage detection later.

Run fine wires through your plastic, pulse the wires, and when you get a reflection you have a break and you can figure where it is.

I'm confused about the application of such a material. If UV light is simply melting the polymer back to together, wouldn't constant UV light from the sun keep the polymer is "melting" form and prevent it from cooling to form the heal? Or would the heal require a special, higher power UV source specifically for healing cuts? How would consumers access such a (possibly dangerous) device?

That's what I'm wondering. Since it reacts in the non-cut form I assume it's the latter, otherwise it'd be unsuitable for almost anything beyond geeking out in the chem lab.

I'm confused about the application of such a material. If UV light is simply melting the polymer back to together, wouldn't constant UV light from the sun keep the polymer is "melting" form and prevent it from cooling to form the heal? Or would the heal require a special, higher power UV source specifically for healing cuts? How would consumers access such a (possibly dangerous) device?

That's what I'm wondering. Since it reacts in the non-cut form I assume it's the latter, otherwise it'd be unsuitable for almost anything beyond geeking out in the chem lab.

Technical facts are great, but I'd like Ars to shed more (UV) light on potential applications of self-healing materials like this. As a consumer, that is what I am interested in.

OK. How about these (in no particular order):

*House coatings that resist hurricanes/tornadoes.*Coatings for your laptop, iPod, cellphone, or whatever.*Replacement for paint on cars. You know that long scratch on your door from the shopping cart that nailed you in the parking lot? Gone after a few hours in sunlight.*Improved body armor for cops*Space exploration: Any "soft" surface like a solar sail could repair itself after being holed by a micrometeorite.*waterproofing your house, or a ship, or fuel tanks. (Granted that last case wouldn't be waterproofing so much as "fuelproofing" but you get the point. And the high levels of heat this process apparently creates would be another cause for concern, but it's still a sound theory.) Also good for things like nuclear reactor holding tanks (both the fuel storage area and the coolant storage tanks).*similar to the waterproofing idea, using it for gaskets around air conditioners, windows, etc. could reduce your heating/cooling costs. It could also be useful to hermetically seal a building against Bad Stuff leaking in or out. (Bad Stuff == Anthrax and other diseases, chemical warfare samples, etc.)

So there are some examples.

One question: Does this mean that a car or building coated in this (or a similar material) would eventually develop scars?

The application that immediately came to me was self-healing structures in zero-atmosphere environments. Like a self-healing shelter on the moon. Being able to immediately reseal a punctured space-suit using a hand-held UV lamp. Possibly sealing the flight surfaces of space structures and vehicles. Such as when loose foam insulation breached the Columbia space shuttle's forward left wing root, causing it to be destroyed on re-entry. I know nothing of the science involved so I may be entirely wrong about any of these uses. Just thinking out loud.

You could possibly make something self-healing with this by coverIng it with a material that has the same melting point, but reflects the frequency that heats it up. Then when the outer skin is damage, the inner is exposed, heating the skin enough so it reflows, covering the internal heating element which then cools back down. The biggest problem I see is getting enough energy through a cut in the skin to the material below. That and matching the materials.